U.S. patent application number 09/992322 was filed with the patent office on 2003-05-08 for lightweight gypsum wallboard and method of making same.
Invention is credited to Conner, Brian D., Seufert, James F., Urban, Carol A., Weir, Richard P..
Application Number | 20030084980 09/992322 |
Document ID | / |
Family ID | 25538190 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030084980 |
Kind Code |
A1 |
Seufert, James F. ; et
al. |
May 8, 2003 |
Lightweight gypsum wallboard and method of making same
Abstract
A method of preparation and use of lightweight, high-strength
gypsum wallboard, as well as a core composition suitable for use
therein, are disclosed. The core composition includes a slurry of
calcium sulfate hemihydrate (stucco), water, acid-modified starch,
and a starch cross-linking agent, having a pH of about 9 to about
11. The composition and method provide a wallboard having a lower
density than conventional wallboard, and with equivalent or better
strength characteristics than conventional wallboard.
Inventors: |
Seufert, James F.; (North
Tonawanda, NY) ; Conner, Brian D.; (Cheektowaga,
NY) ; Urban, Carol A.; (Eden, NY) ; Weir,
Richard P.; (Kenmore, NY) |
Correspondence
Address: |
Howrey Simon Arnold & White, LLP
750 Bering Drive
Houston
TX
77057-2198
US
|
Family ID: |
25538190 |
Appl. No.: |
09/992322 |
Filed: |
November 6, 2001 |
Current U.S.
Class: |
156/39 ; 106/772;
423/171; 423/535 |
Current CPC
Class: |
C04B 24/383 20130101;
Y02W 30/91 20150501; E04C 2/043 20130101; C04B 24/38 20130101; C04B
2111/00112 20130101; C04B 2111/0062 20130101; C04B 28/14 20130101;
C04B 28/14 20130101; C04B 18/241 20130101; C04B 22/06 20130101;
C04B 22/148 20130101; C04B 24/226 20130101; C04B 24/383 20130101;
C04B 38/10 20130101; C04B 28/14 20130101; C04B 18/241 20130101;
C04B 22/0013 20130101; C04B 22/148 20130101; C04B 24/226 20130101;
C04B 24/383 20130101; C04B 38/10 20130101; C04B 28/14 20130101;
C04B 18/241 20130101; C04B 22/148 20130101; C04B 22/16 20130101;
C04B 24/226 20130101; C04B 24/383 20130101; C04B 38/10 20130101;
C04B 28/14 20130101; C04B 18/241 20130101; C04B 22/064 20130101;
C04B 22/148 20130101; C04B 24/226 20130101; C04B 24/383 20130101;
C04B 38/10 20130101; C04B 28/14 20130101; C04B 18/241 20130101;
C04B 22/0013 20130101; C04B 22/148 20130101; C04B 24/226 20130101;
C04B 24/38 20130101; C04B 38/10 20130101; C04B 28/14 20130101; C04B
18/241 20130101; C04B 22/06 20130101; C04B 22/148 20130101; C04B
24/226 20130101; C04B 24/38 20130101; C04B 38/10 20130101; C04B
28/14 20130101; C04B 18/241 20130101; C04B 22/064 20130101; C04B
22/148 20130101; C04B 24/226 20130101; C04B 24/38 20130101; C04B
38/10 20130101; C04B 28/14 20130101; C04B 18/241 20130101; C04B
22/148 20130101; C04B 22/16 20130101; C04B 24/226 20130101; C04B
24/38 20130101; C04B 38/10 20130101 |
Class at
Publication: |
156/39 ; 106/772;
423/171; 423/535 |
International
Class: |
C04B 011/00 |
Claims
What is claimed is:
1. A composition for use in the manufacture of gypsum construction
materials, the composition comprising: at least about 40 wt. %
calcium sulfate hemihydrate, based on the total weight of the
composition; starch; a starch cross-linking agent; and sufficient
water to form a slurry; wherein the pH of the composition is about
9 to about 11.
2. The composition of claim 1, wherein the composition comprises
about 40 wt. % calcium sulfate hemihydrate to about 60 wt. %
calcium sulfate hemihydrate, based on the total weight of the
composition.
3. The composition of claim 1, wherein the composition comprises
about 40 wt. % calcium sulfate hemihydrate to about 55 wt. %
calcium sulfate hemihydrate, based on the total weight of the
composition.
4. The composition of claim 1, wherein the starch is a cationic
starch.
5. The composition of claim 1, wherein the starch is an
acid-modified starch.
6. The composition of claim 1, wherein the starch is an
acid-modified corn starch.
7. The composition of claim 6, wherein the acid-modified corn
starch is present in an amount of about 0.6 wt. % to about 1 wt. %,
based on the weight of the calcium sulfate hemihydrate.
8. The composition of claim 1, wherein the starch cross-linking
agent is present in an amount of about 12 wt. % to about 25 wt. %,
based on the weight of the starch.
9. The composition of claim 1, wherein the starch cross-linking
agent is selected from the group consisting of magnesium oxide,
sodium metaborate, potassium tripolyphosphate, borax, sodium
metaborate hydrate, boric acid, type N hydrated lime, and
combinations thereof.
10. The composition of claim 1, wherein the starch cross-linking
agent is type N hydrated lime, present in an amount of about 12 wt.
% to about 25 wt. %, based on the weight of the starch.
11. The composition of claim 1, wherein the starch cross-linking
agent is type N hydrated lime, present in an amount of about 15 wt.
% to about 25 wt. %, based on the weight of the starch.
12. The composition of claim 1, wherein the composition has a pH of
about 10.8 or less.
13. The composition of claim 10, further comprising aluminum
sulfate.
14. The composition of claim 13, wherein the pH of the composition
is about 9 to about 11.
15. The composition of claim 13, wherein the starch cross-linking
agent is present in the form of type N hydrated lime and the
aluminum sulfate is present in an amount about equal by weight to
the type N hydrated lime.
16. The composition of claim 1, further comprising cellulosic
fiber.
17. The composition of claim 1, further comprising paper fiber.
18. The composition of claim 17, wherein the paper fiber is present
in an amount of about 0.5 wt. % to about 0.75 wt. %, based on the
weight of the calcium sulfate hemihydrate.
19. The composition of claim 1, further comprising a foaming
agent.
20. The composition of claim 19, wherein the foaming agent is
present in an amount of about 0.03 wt. % to about 0.08 wt. %, based
on the weight of the calcium sulfate hemihydrate.
21. The composition of claim 1, further comprising a
dispersant.
22. The composition of claim 1, further comprising naphthalene
sulfonate.
23. The composition of claim 22, wherein the naphthalene sulfonate
is present in an amount of about 0.15 wt. % to about 0.4 wt. %,
based on the weight of the calcium sulfate hemihydrate.
24. A wallboard panel comprising: a first cover sheet; a second
cover sheet; and a core disposed between the first cover sheet and
the second cover sheet, the core comprising calcium sulfate
dihydrate and starch.
25. The wallboard panel of claim 24, wherein the panel has a
substantially uniform thickness of about 1/2 inch, and the density
of the panel is about 1,500 lb/MSF to about 1,700 lb/MSF.
26. The wallboard panel of claim 24, wherein the core comprises at
least about 90 wt. % calcium sulfate dihydrate, based on the weight
of the core.
27. The wallboard panel of claim 24, wherein the starch is a
cationic starch.
28. The wallboard panel of claim 24, wherein the starch is an
acid-modified starch.
29. The wallboard panel of claim 24, wherein the starch is a
cross-linked acid-modified starch.
30. The wallboard panel of claim 24, wherein the starch is a
cross-linked acid-modified corn starch.
31. The wallboard panel of claim 30, wherein the cross-linked
acid-modified corn starch is present in an amount of about 1 wt. %
to about 2 wt. %, based on the weight of the core.
32. The wallboard panel of claim 24, wherein the core further
comprises aluminum sulfate.
33. The wallboard panel of claim 32, wherein the aluminum sulfate
is present in an amount of about 0.15 wt. % to about 0.35 wt. %,
based on the weight of the core.
34. The wallboard panel of claim 24, wherein the core further
comprises cellulosic fiber.
35. The wallboard panel of claim 24, wherein the core further
comprises paper fiber.
36. The wallboard panel of claim 35, wherein the paper fiber is
present in an amount of about 0.4 wt. % to about 0.6 wt. %, based
on the weight of the core.
37. The wallboard panel of claim 24, wherein the core further
comprises a foaming agent.
38. The wallboard panel of claim 37, wherein the foaming agent is
present in an amount of about 0.03 wt. % to about 0.8 wt. %, based
on the weight of the core.
39. The wallboard panel of claim 24, wherein the core further
comprises a dispersant.
40. The wallboard panel of claim 24, wherein the core further
comprises naphthalene sulfonate.
41. The wallboard panel of claim 40, wherein the naphthalene
sulfonate is present in an amount of about 0.15 wt. % to about 0.4
wt. %, based on the weight of the core.
42. The wallboard panel of claim 24, wherein the core comprises: at
least about 90 wt. % calcium sulfate dihydrate; about 1.0 wt. % to
about 2 wt. % cross-linked, acid-modified starch; about 0.15 wt. %
to about 0.35 wt. % aluminum sulfate; about 0.4 wt. % to about 0.6
wt. % paper fiber; about 0.15 wt. % to about 0.4 wt. % naphthalene
sulfonate; and about 0.03 wt. % to about 0.8 wt. % of a foaming
agent, all based on the weight of the core.
43. A method of producing a gypsum wallboard, the method
comprising: forming a slurry comprising water, calcium sulfate
hemihydrate, starch, and a starch cross-linking agent; mixing the
slurry; and depositing the slurry on a cover sheet.
44. The method of claim 43, wherein the starch is a cationic
starch.
45. The method of claim 43, wherein the starch is an acid-modified
starch.
46. The method of claim 43, wherein the starch is a cross-linked
acid-modified starch.
47. The method of claim 43, wherein the starch is a cross-linked
acid-modified corn starch.
Description
FIELD OF THE INVENTION
[0001] The invention generally relates to the production of
lightweight gypsum-containing products and, more specifically, the
invention relates to a method and composition for producing
lightweight gypsum wallboard and related products.
BACKGROUND OF THE INVENTION
[0002] A common method of constructing walls and barriers includes
the use of inorganic wallboard panels or sheets, such as gypsum
wallboard, often referred to simply as "wallboard" or "drywall."
Wallboard can be formulated for interior, exterior, and wet
applications. The use of wallboard, as opposed to conventional
boards made from wet plaster methods, is desirable because the
installation of wallboard is ordinarily less costly and less
cumbersome than installation of conventional plaster walls.
[0003] Walls and ceilings made with gypsum wallboard panels
typically are constructed by securing, e.g., with nails or screws,
the wallboard panels to structural members, such as vertically- and
horizontally-oriented pieces of steel or wood often referred to as
"studs."
[0004] Generally, wallboard is produced by enclosing a core
composition including an aqueous slurry of calcined gypsum and
other materials ("core composition") between two large sheets of
board cover paper (also called surface paper). Various types of
cover paper are used, depending on the particular application.
After the core composition has set (i.e., reacted with water
present in the aqueous slurry) and dried, the formed sheet is cut
into standard sizes. Methods for the production of gypsum wallboard
generally are described, for example, by T. Michelsen, "Building
Materials (Survey)," Encyclopedia of Chemical Technology, (1992 4th
ed.), vol. 21, pp. 621-24, TP9.E685, the disclosure of which is
hereby incorporated herein by reference.
[0005] Gypsum wallboard is manufactured utilizing commercial
processes that are capable of operation under continuous,
high-speed conditions. A conventional process for manufacturing the
core composition of gypsum wallboard initially includes the
premixing of dry ingredients in a high-speed mixing apparatus. The
dry ingredients can include calcium sulfate hemihydrate, an
accelerator, and a binder (e.g., starch). The dry ingredients are
mixed together with a "wet" (aqueous) portion of the core
composition in a pin mixer apparatus. The wet portion can include a
first component, commonly referred to as a "paper pulp solution,"
that includes a mixture of water, paper pulp, and, optionally, one
or more fluidity-increasing agents, and a set retarder. The paper
pulp solution provides a major portion of the water that forms the
gypsum slurry of the core composition. A second wet component can
include a mixture of foam and other conventional additives, if
desired. Together, the aforementioned dry and wet portions comprise
an aqueous gypsum slurry that forms a core composition.
[0006] A major ingredient of the core composition is calcium
sulfate hemihydrate, commonly referred to as "calcined gypsum,"
"stucco," or "plaster of Paris." Stucco has a number of desirable
physical properties including, but not limited to, its fire
resistance, thermal and hydrometric dimensional stability,
compressive strength, and neutral pH. Typically, stucco is prepared
by drying, grinding, and calcining natural gypsum rock (i.e.,
calcium sulfate dihydrate). Typical impurities found in the natural
gypsum rock include impurities such as clay, quartz, dirt, sand,
sodium chloride, calcium chloride, and dolomitic limestone. The
drying step of stucco manufacture includes passing crude gypsum
rock through a rotary kiln to remove any free moisture present in
the rock from rain or snow, for example. The dried rock then is
passed through a roller mill (or impact mill types of pulverizers),
wherein the rock is ground or comminuted to a desired fineness. The
degree of comminution is determined by the ultimate use. The dried,
fine-ground gypsum can be referred to as "land plaster" regardless
of its intended use. The land plaster is used as feed to
calcination processes for conversion to stucco.
[0007] The calcination (or dehydration) step in the manufacture of
stucco is performed by heating the land plaster, and generally can
be described by the following chemical equation which shows that
heating calcium sulfate dihydrate yields calcium sulfate
hemihydrate (stucco) and water vapor:
CaSO.sub.4.2H.sub.2O+heat.fwdarw.CaSO.sub.4.1/2H.sub.2O+11/2H.sub.2O.
[0008] This calcination process step is performed in a "calciner,"
of which there are several types known by those of skill in the
art.
[0009] Uncalcined calcium sulfate (i.e., land plaster) is the
"stable" form of gypsum. However, calcined gypsum, or stucco, has
the desirable property of being chemically reactive with water, and
will "set" rather quickly when the two are mixed together. This
setting reaction is actually a reversal of the above-described
chemical reaction performed during the calcination step. The
setting reaction proceeds according to the following chemical
equation which shows that the calcium sulfate hemihydrate is
rehydrated to its dihydrate state:
CaSO.sub.4.1/2H.sub.2O+11/2H.sub.2O.fwdarw.CaSO.sub.4.2H.sub.2O+heat.
[0010] The actual time required to complete the setting reaction
generally depends upon the type of calciner and the type of gypsum
rock that are used to produce the gypsum, and can be controlled
within certain limits by the use of additives such as retarders,
set accelerators, and/or stabilizers, for example. Generally, the
rehydration time period can be in a range of about two minutes to
about eight hours depending on the amount and quality of retarders,
set accelerators, and/or stabilizers present.
[0011] After the aqueous gypsum slurry is prepared, the slurry and
other desired ingredients are combined to form a core composition
that is continuously deposited to form a wallboard core between two
continuously-supplied moving sheets of board cover paper. The two
cover sheets generally comprise a pre-folded face paper and a
backing paper. As the core composition is deposited onto the face
paper, the backing paper is brought down atop the deposited core
composition and bonded to the pre-folded edges of the face paper.
The whole assembly then is sized for thickness utilizing a roller
bar or forming plate. The deposited core composition is then
allowed to set between the two cover sheets, thereby forming a
gypsum wallboard. The continuously-produced board is cut into
panels of a desired length and then passed through a drying kiln
where excess water is removed to form a strong, dry, and rigid
building material.
[0012] The cover sheets used in the process typically are multi-ply
paper manufactured from re-pulped newspapers and/or other grades of
recycled papers. The face paper has an unsized inner ply which
contacts the core composition such that gypsum crystals can grow up
to (or into) the inner ply--this, along with the starch, is the
principal form of bonding between the core composition and the
cover sheet. The middle plies are sized and an outer ply is more
heavily sized and treated to control absorption of paints and
sealers. The backing paper is also a similarly constructed
multi-ply sheet. Both cover sheets must have sufficient
permeability to allow for water vapor to pass through them during
the downstream board drying step(s).
[0013] Standardized sheets (or panels) of wallboard typically are
cut and trimmed to dimensions of about four feet (about 1.2 meters)
wide and about 8 feet to about 16 feet (about 2.4 meters to about
4.9 meters) in length (ASTM-C36). Sheets typically are available in
thicknesses varying in a range of about 1/4 inch to about one inch
(about 0.635 centimeters (cm) to about 2.54 cm) in about 1/8 inch
(about 0.3175 cm) increments.
[0014] The time at which the board may be cut, or in other words,
the speed of the conveyor and the consequent rate of production of
the gypsum board, is generally controlled by the setting time of
the calcined gypsum slurry. Thus, conventional adjuvants to the
calcined gypsum slurry in the mixer generally include set time
control agents, particularly accelerators. These and other
additives, such as pregenerated foam to control final density of
the board, paper cover sheet bond promoting agents, fibrous
reinforcements, consistency reducers and the like typically
constitute less than 5%, and usually less than 2%, of the weight of
the finished board core.
[0015] Numerous compositions and methods of production of
wallboards have been disclosed.
[0016] U.S. Pat. No. 5,641,584 (issued Jun. 24, 1997) offers
mixtures of cement, a rheology modifying agent, and a lightweight
aggregate material for use as an insulating material. The materials
may further contain fibrous materials.
[0017] U.S. Pat. No. 5,922,447 (issued Jul. 13, 1999) suggests
gypsum boards containing gypsum, perlite, and starch. The starch is
used to act as a binder for binding the gypsum to the perlite.
[0018] U.S. Pat. No. 5,888,322 (issued Mar. 30, 1999) offers
methods for preparing gypsum wallboard containing polymeric
oxyalkylate viscosity modifiers. The use of various polymers and
copolymers are suggested.
[0019] U.S. Pat. No. 5,305,577 (issued Apr. 26, 1994) suggests fire
resistant cores containing gypsum dihydrate, paper fiber, and
performance boosters (inorganic fiber, clay, vermiculite, or binder
polymer). Structures containing the core have at least a 20 minute
ASTM E-152 fire test rating.
[0020] U.S. Pat. Nos. 4,916,004 and 5,221,386 offer methods for the
continuous production of wallboards containing cement cores
strengthened by a mesh of reinforcing fibers.
[0021] U.S. Pat. No. 5,342,566 (issued Aug. 30, 1994) proposes
methods and apparatus for the production of gypsum boards. The
method included mixing fibers, absorbent, and water to form a
mixture, mixing the wetted fibers with dry calcined gypsum, forming
the resulting mixture into a matt, and compressing the matt to
produce a gypsum board.
[0022] U.S. Pat. No. 3,952,830 (issued Apr. 27, 1976) describes
acoustical panels containing expanded volcanic glass, mineral
fibers, cellulosic fiber, and binder and sizing agents. The fibers
act to hold the perlite particles in position during the
manufacturing process, and creates an interconnected network of
voids.
[0023] U.S. Pat. No. 4,019,920 (issued Apr. 26, 1977) describes
mixtures of gypsum and starch which function as an accelerator for
the setting reaction of calcined gypsum and water.
[0024] U.S. Pat. No. 4,350,533 (issued Sep. 21, 1982) offers
mixtures of high alumina cement, gypsum, lime, and water for use in
preparing high early strength cement. Early stages of hydration
produces ettringite.
[0025] U.S. Pat. No. 5,879,446 (issued Mar. 9, 1999) suggests core
compositions and methods for the production of gypsum wallboards.
The core compositions contain a slurry of calcium sulfate
hemihydrate, water, and calcium aluminum lignosulfonate and/or
aluminum lignosulfonate. The compositions can be supplemented with
paper fibers, corn starch, or potash.
[0026] U.S. Pat. No. 5,277,712 (issued Jan. 11, 1994) offers a
drywall panel joint compound containing fine plaster, alkyl
cellulose, perlite, and a set time retarding agent. The joint
compound exhibits flexural strength of at least 50 pounds/lineal
inch, minimum shrinkage, and substantially no visible cracking
under hot and dry atmospheric conditions.
[0027] U.S. Pat. No. 4,174,230 (issued Nov. 13, 1979) suggests the
preparation of gypsum compositions comprising at least one binder
selected from the group consisting of a water-soluble organic
polymer, a water-dispersible organic polymer, a water-soluble
inorganic compound, a water-dispersion medium colloid-forming
inorganic compound, a water-hardenable compound and a mixture
thereof. The composition is used in lightweight gypsum moldings
which exhibit great mechanical strength.
[0028] Standardized sheets of wallboard typically have a density in
a range of about 1,600 pounds (lbs.) to about 1,800 lbs. per
thousand square feet (lbs/MSF) (about 7,800 kilograms (kg) to about
8,300 kg per thousand square meters (m.sup.2)) of about one-half
inch (1.27 cm) board. Heavy or high-density gypsum wallboards are
more costly and difficult to manufacture, transport, store, and
manually install at job sites, compared to lighter or low-density
boards. It is possible to formulate wallboard having reduced
densities through the inclusion of lightweight fillers and foams,
for example. Often, however, where wallboard is formulated to have
a density less than about 1,600 lbs/MSF (about 7,800 kg per 1,000
m.sup.2) of about one-half inch (1.27 cm) board, the resulting low
strength makes the board unacceptable for commercial sale. Because
high-density or heavy gypsum wallboard generally is not desirable,
various attempts have been made to reduce board weight and density
without sacrificing board strength. However, while lighter and less
dense wallboard products can be produced, many of the wallboard
products may be of a quality ill-suited for commercial use.
[0029] One type of gypsum wallboard panel product failure occurs
when a fastener head, such as a nail head, is pulled through the
gypsum wallboard panel. The strength measure of a gypsum wallboard
panel for this type of failure is known as nail pull resistance.
Standardized tests to measure nail pull resistance (e.g. ASTM C
473-00), typically measure the ability of a gypsum wallboard panel
to resist pull-through of a standard size nail head through the
product.
[0030] Another measure of gypsum wallboard panel strength is its
compressive strength, which is its ability to resist compressive
forces. Compressive strength also is an indirect measure of other
strength properties such as transverse load strengths, sag
resistance, 90.degree. pull force resistance, and core tensile
strength, for example.
[0031] In view of the foregoing, it would be desirable to produce
high-strength gypsum wallboard having weights and densities
generally equal to or slightly less than those produced by
conventional methods. Reduced weight and density boards, however,
should meet industry standards and have strengths similar to, or
greater than, conventional wallboard of higher density. Such
wallboard also should be able to be manufactured using high-speed
manufacturing apparatus and not suffer from other negative
side-effects. For example, such high-strength wallboard should be
able to set and dry within a commercially reasonable period of
time.
SUMMARY OF THE INVENTION
[0032] It is an object of the invention to overcome one or more of
the problems described above.
[0033] Thus, one aspect of the invention is a composition for use
in the manufacture of gypsum construction materials including
calcium sulfate hemihydrate, acid-modified starch, a starch
cross-linking agent, and sufficient water to form a slurry, having
a pH of about 9 to about 11.
[0034] Another aspect of the invention is a method of making a
composition for use in gypsum board manufacturing processes. The
method generally includes the steps of: forming a slurry including
water, acid-modified starch, a starch cross-linking agent, and
calcium sulfate hemihydrate, having a pH of about 9 to about 11;
and mixing the slurry.
[0035] Yet another aspect of the invention is a wallboard panel
which includes a first cover sheet, a second cover sheet, and a
core disposed between the cover sheets, wherein the core includes
calcium sulfate dihydrate, and cross-linked, acid-modified
starch.
[0036] Still another aspect of the invention is a method of
producing gypsum wallboard. The method generally includes the step
of forming a slurry containing water, calcium sulfate hemihydrate,
acid-modified starch, and a starch cross-linking agent, having a pH
of about 9 to about 11. The method also includes the steps of
mixing the slurry, and depositing the slurry on a cover sheet.
[0037] Further aspects and advantages of the invention may become
apparent to those skilled in the art from a review of the following
detailed description, taken in conjunction with the appended
claims.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Generally, the invention is directed to a composition for
use in the manufacture of gypsum construction materials, such as
gypsum wallboard. The term "core composition" will be used to refer
to the wet slurry containing calcium sulfate hemihydrate that is
useful in producing a wallboard article, and to the term "wallboard
core" will be used to refer to the hardened (i.e., set) material
containing calcium sulfate dihydrate. The core composition includes
calcium sulfate hemihydrate, acid-modified starch, a starch
cross-linking agent, and sufficient water to form a slurry. The
invention also is directed to gypsum wallboard panels, methods of
making the core composition, and methods of making gypsum wallboard
panels.
[0039] The core composition of the invention provides improvements
in properties of a wallboard core and wallboard article, such as
increased strength per unit density and improved bonding between
the paper cover sheet and the wallboard core. Core compositions and
wallboard cores made according to the invention can be made lighter
in weight (i.e., lower density) and with the same or better
strength characteristics as typical, heavier (i.e., more dense)
wallboard.
[0040] The ingredients of a preferred core composition of the
invention will now be described in more detail. One dry ingredient
present in a core composition of the invention is calcium sulfate
hemihydrate, or stucco (CaSO.sub.4.1/2H.sub.2O). Preferably, the
.beta.-hemihydrate form of calcium sulfate hemihydrate is used in
the invention, however, either the .alpha.- or .beta.-form may be
used. The core composition includes at least about 40 wt. % calcium
sulfate hemihydrate, preferably up to about 60 wt. %, more
preferably at least about 35 wt. % and up to about 55 wt. %, and
even more preferably at least about 40 wt. % and up to about 55 wt.
%, for example about 48 wt. % calcium sulfate hemihydrate, based on
the total weight of the core composition. The calcium sulfate
hemihydrate can be produced by a dry calcination method, such as
kettle, Calcidyne, Holo-flite, rotary kiln, Imp Mill, or Claudius
Peters calcination. The calcium sulfate hemihydrate can also be
produced by wet calcination methods.
[0041] The core composition also includes a starch, which functions
as a binder within the wallboard core and at the interface of the
wallboard core and a cover sheet. Different types of starches may
be used in the wallboard core. Typically, wallboard binders are
manufactured from starches made from corn, wheat, or milo.
Non-modified starches such as pearl starch may be used in the
inventive compositions and methods. Cationic starches work well on
a pound per pound basis as compared to other starches, but are
currently relatively expensive. Acid-modified starches are
attractive due to their current low cost relative to other
commercially available starches. Acid-modified starch is typically
available as a dry powder, and can be added with other dry
ingredients, in a liquid pulp solution, or in a separate liquid
feed. Without intending to be bound by any particular theory, it is
believed that the advantages of the invention are achieved by
lowering the gelatinization temperature of the starch, so that the
starch can migrate faster and deposit more starch at the cover
paper/core interface, and also by cross-linking the starch to
solidify it and prevent it from completely migrating out of the
core. Any acid-modified starch suitable in typical gypsum
construction materials (such as wallboards, mortars, and joint
compounds) can be used in a core composition according to the
invention. Acid-modified corn starch is a widely available
material. A suitable starch for the invention is an acid-modified
(also called "acid hydrolyzed") starch sold as Wallboard Binder
Starch, CAS #65996-63-6, by A. E. Staley Manufacturing Co., of
Decatur, Ill.
[0042] The amount of starch used in a core composition and
wallboard core according to the invention is generally greater than
the amount of starch used in typical gypsum construction materials,
and particularly greater than the amount used in conventional
wallboard.
[0043] The core composition preferably includes at least about 0.5
wt. % acid-modified starch, preferably up to about 1.5 wt. %, more
preferably at least about 0.6 wt. % and up to about 1 wt. %, for
example about 0.8 wt. % acid-modified starch, based on the total
weight of the core composition. When the core composition sets, the
relative amount of starch will increase slightly due to loss of
water on drying.
[0044] Any chemical that cross-links a starch added to the core
composition can be used in the invention. Various starch
cross-linking agents are known in the art. Suitable starch
cross-linking agents include sodium metaborate, potassium
tripolyphosphate, borax, sodium metaborate hydrate, boric acid,
magnesium oxide, type N hydrated lime, and combinations thereof.
Magnesium oxide and type N hydrated lime are preferred,
particularly type N hydrated lime.
[0045] Type N dolomitic hydrated lime is primarily a mixture of
about 48 wt. % calcium oxide, about 31 wt. % magnesium oxide, and
chemically combined water. Since type N dolomitic hydrates are
derived from dolomitic quicklime (which, in turn, is derived from
limestone containing about 35 wt. % to about 46 wt. % magnesium
carbonate) hydrated under atmospheric pressure, water is combined
only with the calcium oxide portion of the lime. Type N hydrated
lime made from high calcium quicklime (derived from limestone
having up to about 5 wt. % magnesium carbonate) and magnesium
quicklime (derived from limestone having about 5 wt. % to about 35
wt. % magnesium carbonate) are also available. A suitable type N
dolomitic hydrated lime is sold under the name GRAND PRIZE finish
lime by Graymont Dolime (OH), Inc. (Genoa, Ohio). When type N
hydrolyzed lime is used, it is preferably added as a dry ingredient
with the stucco.
[0046] A starch cross-linking agent is added in an amount
sufficient to cross-link the starch to create a substantially solid
starch (e.g., thicker than a typical "thick boiling" starch) before
the starch has the time to completely migrate out of the core
composition to the cover paper/core interface. Generally, a starch
cross-linking agent is present in the core composition in a range
of at least about 10 wt. % and up to about 30 wt. %, preferably at
least about 12 wt. % and up to about 25 wt. %, based on the weight
of the acid-modified starch.
[0047] Without intending to be bound by any particular theory, it
is believed that raising the pH of the core composition lowers the
gelatinization temperature of the starch and increases its
mobility. For example, a typical acid-modified corn starch used as
a wallboard binder has a gelatinization temperature of about 160 to
about 170.degree. F., for example about 162.degree. F. In cooked
form, the typical starch is thin boiling (i.e., thin and syrup-like
when cooking is completed) but it turns to a soft gel when cooled.
In contrast, it has been found that an acid-modified corn starch
mixed with type N hydrated lime has a gelatinization temperature of
about 140.degree. F. to about 150.degree. F., for example about
142.degree. F. In cooked form, this acid-modified starch is
solidified (i.e., is thicker than a typical "thick boiling"
starch), and syneresis is evident upon cooling of the cooked
starch. In this example, it is believed that the calcium hydroxide
component of the type N hydrated lime contributes to the affect
upon gelatinization temperature, and the magnesium oxide component
of the type N hydrated lime contributes to the cross-linking of the
starch. Various other compounds can be used to raise the pH of the
core composition, but calcium hydroxide (present as type N hydrated
lime) is preferred.
[0048] When using type N hydrated lime as a starch cross-linking
agent, the pH of the core composition can be made too high. For
example, as the pH is raised above about 11.2, the wet bond between
a cover sheet and the core composition is reduced to the point
where high-speed board manufacture is nearly impossible at a pH of
about 12. Preferably, the pH of the core composition is about 10.8
or less. A minimum pH of the core composition of about 9 is
preferred, and a pH in the range of about 10 to about 10.4, for
example about 10.2, is more preferred.
[0049] Various additives (such as inorganic acids) can be used to
reduce the pH of the core composition, but alum (aluminum sulfate)
is preferred. When type N hydrated lime is used, aluminum sulfate
is present preferably in an amount about equal by weight to said
type N hydrated lime. Alum is available as a solid or in an aqueous
liquid solution, such as by General Chemical Corporation of
Parsipany, N.J. When added to the core composition as a solid, it
preferably is fed with the stucco and other dry ingredients; when
added as a liquid, it preferably is metered to the mixer as an
independent feed.
[0050] Various other ingredients, such as paper fibers and foaming
agents, can be used in the core composition to provide additional
strength and flexibility and to further reduce the density of the
wallboard, while maintaining strength. In similar fashion, other
additives can be used to facilitate the manufacturing process, such
as dispersants (also known as water reducing agents) and gypsum set
accelerators. These optional ingredients will be discussed
below.
[0051] Cellulosic fibers, such as paper fibers preferably are added
to the core composition, most preferably with other additives in an
aqueous pulp slurry or solution. Preferably, a paper pulp solution
provides a major portion of the water that forms the slurry of the
core composition. The water supplied to the core composition should
include sufficient water for the setting reaction of the gypsum,
plus an additional amount sufficient to decrease the consistency of
the slurry during the manufacturing process. The cellulosic fibers
preferably are paper fibers, more preferably and conveniently
derived from ground wallboard paper cover sheet offstock.
[0052] The cellulosic fibers in the pulp solution serve to enhance
the flexibility and overall strength of the gypsum wallboard.
Gypsum wallboard made without fibers is typically very brittle and
more susceptible to breakage during handling. The cellulosic fibers
aid in evenness of drying during manufacture, and enhance the
ability of the final wallboard article to accept and hold nails
during installation.
[0053] Generally, cellulosic fibers are present in a core
composition and wallboard core of the invention in greater amounts
than in typical gypsum wallboard construction. Thus, when paper
fiber is used it is preferably present in an amount of at least
about 0.5 wt. % and up to about 0.75 wt. %, based on the weight of
the calcium sulfate hemihydrate. Put another way, paper fiber
preferably is present in an amount of about 0.4 wt. % to about 0.6
wt. %, based on the weight of a wallboard core.
[0054] Wet ingredients used to make the core composition preferably
include a foaming agent (i.e., soap). Foam introduces air voids
into the core through the use of a foaming agent that contains very
little solid material, but is resilient enough to resist
substantial breakdown in the mixing operation. In this manner, the
density of the core can be reduced in a controlled manner. A
foaming agent can be supplied in either liquid or flake (powdered)
form, and can be produced from various soaps, including those known
in the art. A suitable foaming agent for the invention is a
sulfated, ethoxylated, primary, linear alcohol mixture which is
described by the chemical formula CH.sub.3(CH.sub.2).sub.xCH.sub-
.2(OCH.sub.2CH.sub.2).sub.yOSO.sub.3.sup.-M.sup.+, wherein x
normally lies in the range of 6 to 8, y ranges between 1.5 and 2.5
(with 2.2 being preferred), and M is selected from the group
consisting of sodium and ammonium, such as CEDEPAL FA-406, sold by
the Stepan Company of Northfield, Ill. See also U.S. Pat. No
4,156,615 (May 29, 1979), the disclosure of which is incorporated
herein by reference.
[0055] Preferably, a foaming agent is present in the core
composition in an amount of at least about 0.01 wt. % and up to
about 0.1 wt. %, more preferably at least about 0.03 wt. % and up
to about 0.08 wt. %, based on the weight of the calcium sulfate
hemihydrate or the weight of the wallboard core. The amount of
foaming agent added can vary depending on the source (and, thus,
quality) of the calcium sulfate hemihydrate (e.g., source of the
land plaster) used to produce the core composition.
[0056] "Water-reducing" additives may be included in the core
composition to improve its fluidity while allowing the use of
reduced levels of water. Reduction in water usage brings reduced
costs in the form of reduced water and energy demands, as less
water will have to be removed during the drying step(s). Reduction
of water usage also provides environmental benefits.
[0057] Various commercially-available dispersants (also known as
fluidity-enhancing and/or water-reducing agents) are known in the
art for various applications. However, lignosulfonate materials,
used as dispersants in other wallboard applications, are to be
avoided in the methods and compositions of the invention.
Fluidity-enhancing and/or water-reducing agents supplied in liquid
form can be either incorporated in the pulp solution or added
directly to the mixing operation. The use of condensation products
of naphthalene sulfonic acid and formaldehyde is preferred. A
suitable water-reducing agent useful in the invention is a sodium
salt of sulfonated naphthalenesulfonate, sold under the trade name
DILOFLO GW, by Geo Chemicals, Inc. (Harrison, N.J.). The use of
higher molecular weight anionic condensation products such as
melamine formaldehyde modified with sulfite alkylaryl sulfonates is
also known. See also U.S. Pat. No. 4,184,887, the disclosure of
which is hereby incorporated herein by reference.
[0058] Water-reducing agents are described in "The Gypsum Industry
and Flue Gas Desulftuization (FGD) Gypsum Utilization: A Utility
Guide," New York State Electric & Gas Corp. and ORTECH, pp.
3-38 (1994), the disclosure of which is hereby incorporated herein
by reference.
[0059] Preferably, a dispersant, such as a naphthalene sulfonate,
is present in an amount of at least about 0.15 wt. % and up to
about 0.4 wt. %, based on the weight of the calcium sulfate
hemihydrate or the wallboard core.
[0060] An accelerator can be used to accelerate the set of calcium
sulfate hemihydrate to calcium sulfate dihydrate and thus produce
the wallboard core from the core composition. Examples of suitable
accelerators, some of which also are available liquid form,
include, but are not limited to, ball milled accelerators ("BMA")
and metallic salts that provide cations, such as aluminum sulfate,
potassium sulfate (sulfate of potash), calcium sulfate, ferrous
sulfate, and ferric chloride supplied, for example, by the J. T.
Baker Chemical Company of Philadelphia, N.J. The preferred
accelerator is a BMA made by combining very finely ground gypsum
(land plaster) with an acid-modified starch in a ball mill, in a
ratio of approximately 1:1. The fine gypsum crystals act as seed
crystals to spur crystal growth, and the starch acts as a flow
agent. Potassium sulfate is also preferred. The amount of
accelerator added can vary depending on the source (and, thus,
quality) of the calcium sulfate hemihydrate (e.g., source of the
land plaster) used to produce the core composition.
[0061] A set retarder optionally may be added with the paper pulp
solution and can be used in conjunction with the aforementioned
accelerator in order to tailor the set time of the core
composition. Set retarding agents are known in the art, and are
made from organic material such as hog's hair, hooves, and the
like, or from chemical polymers which provide similar
functionality. Set retarding agents are typically used in the
invention at very low concentrations such as, for example, about
0.01 wt. %, based on the weight of the calcium sulfate hemihydrate
or the wallboard core, or about 0.005 wt. %, based on the weight of
the core composition.
[0062] In some embodiments, lightweight aggregates (e.g., expanded
perlite or vermiculite) also can be included.
[0063] A pulp solution can be prepared, for example, by blending or
mixing cellulosic fiber, dispersant, set retarder, and starch with
water in a blending apparatus. Alternatively, a concentrated pulp
solution using only a small volume of water can be produced. In
this case, the remainder of the core mix water requirement is made
up with a separate water source. Typically, about 75 weight parts
water are used per 100 weight parts stucco. Preferably, high shear
mixing "pulps" the material, forming a homogenous solution or
slurry. The pulp solution can be transferred to a holding vessel,
from which it can be continuously added to the core composition
mix.
[0064] Gypsum wallboard can be adapted for wet and exterior
applications, in addition to use in constructing interior walls and
ceilings. In the production of production of exterior sheathing and
moisture-resistant board cores, various materials can be
incorporated into the core composition to impart increased
absorption resistance to the board. Useful materials include
silicone and other water repellents, waxes, and asphalt emulsions.
These materials are typically supplied as water emulsions to
facilitate ease of incorporation into the board core. These
materials can be added directly into the mixing apparatus or
incorporated into the pulp solution prior to addition to the mixing
apparatus.
[0065] The invention is not limited to any order or manner of
mixing the ingredients described above.
[0066] Approximate ranges and specific examples (in brackets) of
amounts of ingredients for a core composition of the prior art and
one embodiment of a core composition according to the invention are
shown in Table I below, wherein the amount of each ingredient is
specified as pounds per thousand square feet of 1/2 inch (1.27 cm)
wallboard (lb/MSF). A panel of 1/2 inch (1.27 cm) wallboard has an
overall thickness of 1/2-inch (1.27 cm) provided by a wallboard
core sandwiched between two cover sheets, each cover sheet having a
thickness of about 13 thousandths of an inch to about 17
thousandths of an inch (about 0.33 mm to about 0.44 mm), for
example about 16 thousandths of an inch (about 0.4 mm).
1TABLE I Ingredient Prior Art Embodiment of Invention stucco 1250
to 1475 [1433.4] 1150 to 1375 [1334.1] water 958 to 1130 [1098.6]
896 to 1072 [1039.7] starch 5.5 to 13.0 [10.0] 15.5 to 23.0 [20.0]
paper fiber 0.0 to 8.0 [2.9] 7.5 to 8.5 [8.0] type N hydrated lime
-- [0.0] 2.5 to 5.0 [2.5] aluminum sulfate -- [0.0] 2.5 to 5.0
[2.5] dispersant 1.0 to 5.5 [2.0] 2.5 to 6.5 [3.0] set accelerator
2.0 to 4.5 [2.5] 2.0 to 4.5 [2.5] dextrose 1.0 to 2.5 [1.4] 1.0 to
2.5 [1.4] foaming agent 0.4 to 1.1 [0.6] 0.4 to 1.1 [0.6] potassium
sulfate 0.25 to 2.5 [0.5] 0.25 to 2.5 [0.5] set retarder 0.10 to
0.20 [0.15] 0.10 to 0.20 [0.15]
[0067] A preferred process for manufacturing the core composition
and wallboard of the invention initially includes the premixing of
dry ingredients in a mixing apparatus. The dry ingredients
preferably include calcium sulfate hemihydrate (stucco), an
optional accelerator, and starch. The dry ingredients are
preferably mixed together with one or more "wet" (aqueous) portions
of the core composition in a pin mixer apparatus. However, the
invention is not limited to the order and manner of mixing the
ingredients described above.
[0068] The core composition thus produced is deposited between
paper cover sheets to form a sandwich. The core composition is
allowed to cure or set, whereby calcium sulfate hemihydrate is
converted to calcium sulfate dihydrate. As described above, the
starch migrates from the core composition to the core/cover sheet
interface, and cross-links. The product then preferably is dried by
exposing the product to heat, in order to remove excess water not
consumed in the reaction forming the calcium sulfate dihydrate.
[0069] The setting reaction produces gypsum crystals, which are
interwoven to contribute strength to the dried wallboard core. The
crosslinked starch preferably bonds the gypsum wallboard core to
the cover sheets, providing an enhanced bond. The cross-linked
starch also preferably contributes to enhanced bond between gypsum
crystals, paper fibers, and other ingredients throughout the
wallboard core. This bonding increases the strength of a wallboard
article and enhances other properties of a wallboard article, such
as resistance to peel and more uniform score and snap
characteristics.
[0070] In order to demonstrate the advantageous results of the
invention, comparative testing has been performed.
[0071] The following examples are included to demonstrate preferred
embodiments of the invention. It should be appreciated by those of
skill in the art that the techniques disclosed in the examples
which follow represent techniques discovered by the inventors to
function well in the practice of the invention, and thus can be
considered to constitute preferred modes for its practice. However,
those of skill in the art should, in light of the present
disclosure, appreciate that many changes can be made in the
specific embodiments which are disclosed and still obtain a like or
similar result without departing from the spirit and scope of the
invention.
EXAMPLES
Example 1
[0072] Samples of 1/2-inch (1.27 cm) wallboard of the prior art and
according to an embodiment of the invention were produced from core
composition prepared in accordance with the specific, examples
described in Table I above. The boards had the constituents and
properties identified in Table II below, wherein the amount of each
ingredient is specified as pounds per thousand square feet (lb/MSF)
of 1/2 inch (1.27 cm) wallboard having cover sheets of about 11
thousandths of an inch (about 0.4 mm).
2 TABLE II Ingredient Prior Art Embodiment of Invention gypsum
1674.9 1558.8 starch 10.0 20.0 paper fiber 2.9 8.0 type N hydrated
lime 0.0 2.5 aluminum sulfate 0.0 2.5 dispersant 2.0 3.0 set
accelerator 2.5 2.5 dextrose 1.4 1.4 foaming agent 0.6 0.6
potassium sulfate 0.5 0.5 set retarder 0.15 0.15 cover sheets 85.0
85.0 TOTAL WEIGHT 1780 1685
[0073] The wallboard produced according to the invention was nearly
100 pounds (45.4 kg) lighter per thousand square feet (per 93
m.sup.2) than the wallboard produced according to the prior art.
The core composition used to produce wallboard according to the
invention had a pH of about 10.
Example 2
[0074] Additional boards were produced on a mass scale according to
the formulations provided in Example I above, except that: (1)
about 12.5 lb/MSF and about 22.5 lb/MSF of acid-modified starch
were used in the boards of the prior art and the invention,
respectively; and (2) about 2.8 lb/MSF and about 8.3 lb/MSF of
paper fiber were used in the boards of the prior art and the
invention, respectively. About 160 prior art boards and 90 boards
according to the invention were produced and tested for various
strength characteristics, as described below. On the day that the
boards according to the prior art formulation were produced, the
average land plaster purity was about 81.1 wt. % calcium sulfate
hemihydrate, the balance (according to typical conditions)
including impurities such as clay, quartz, dirt, sand, sodium
chloride, calcium chloride, and dolomitic limestone; dolomitic
limestone was a significant portion of the impurities. On the day
that the boards according to the invention were produced, the
average land plaster purity was about 80.1 wt. % calcium sulfate
hemihydrate, the balance (according to typical conditions)
including impurities such as clay, quartz, dirt, sand, sodium
chloride, calcium chloride, and dolomitic limestone; dolomitic
limestone was a significant portion of the impurities. The core
composition used to produce boards according to the invention had a
pH in the range of about 9.8 to about 10.2.
[0075] Comparative testing was performed on the wallboards produced
as described above for various characteristics of strength and
quality, including tests on "nail pull resistance," "end peel,"
"score and snap," "shear width," "shear split," and "humidified
bond."
[0076] Nail pull resistance testing measures the ability of a
gypsum wallboard panel to resist pull-through of a standard size
nail head through the product. Nail pull tests were conducted on
the samples according to ASTM C 473-00, Method A, the disclosure of
which is hereby incorporated herein by reference.
[0077] End peel tests were performed to quantify the degree of
paper-to-core bond failure at the ends of the wallboard. To perform
the test, the face paper at the board end is grasped with a thumb
and index finger, the thumbnail is inserted into the board core at
the end (to take a "bite" of core), and the face paper is peeled
back in the machine direction (i.e., perpendicular to the width)
until it tears through the topliner paper ply. The procedure is
repeated at approximately 12 inches, 24 inches, and 36 inches
across the width of the board, on both the front and back sides of
the board, and the maximum value is reported.
[0078] Common wallboard installation practice involves scoring one
side of a gypsum wallboard, snapping the core at the score line,
and back-snapping the unscored paper. Normally, the back-snapping
is done by merely pulling the board toward the scored side to
separate the board into two pieces. Board quality relative to this
test is evaluated by how smooth, straight, and free of protrusions
from the core that the snapped edge is and whether the wallboard
core integrity is compromised. The test is performed on board
samples that are "hot" at the takeoff of the production line.
Because flexing a wallboard can produce knobby scores by causing
microscopic stress cracking in the core, to simulate normal
handling condition a second board sample is pre-flexed by lifting a
board at opposing ends high enough that the center of the board is
suspended above the working surface. To perform the test, the board
is scored on the back, across the full width (perpendicular to the
paperbound edges, using a square), 36 inches in from a mill cut
end. The sample is then snapped at the score line, and then the
36-inch section is folded back until it is at a 90 degree angle
from the remainder of the board. Finally, the board is unfolded so
that it is flat again, and the 36-inch section is pulled up
(back-snapped, toward the back of the board) to separate the board
into two pieces. The end of the 36-inch board section is examined
to measure core protrusions, i.e., the maximum distance that any
portion of the gypsum core extends out beyond the score line.
[0079] The shear width and shear split tests are used to gauge
wallboard core integrity, quality of drying conditions, and degree
of bond between the wallboard core and surface papers. To perform
the tests, a full-width piece of wallboard (e.g., 48 inches) is
manually broken into two piece, and the broken edges (generally
wedge-shaped) of the two broken ends are evaluated for shear width
and shear split. Shear width (in inches) is the greatest linear
distance from the end of one surface paper to the end of the
opposing surface paper across the broken edge of wallboard,
measured in a direction parallel to the major plane of a wallboard
piece and perpendicular to the broken end of a wallboard piece.
Shear split (in inches) is a measure of separation between the
wallboard core and surface papers at the broken ends, and is the
average of the greatest linear distance (front and back surface
papers) of separation, measured in the same direction as shear
width. Each test is performed on a board still hot from the
take-off of production and again after a board has been conditioned
overnight (at least 12 hours) at warehouse conditions.
[0080] The humidified bond test measures the degree of bond (and
bond failure) between a wallboard core and surface papers of a
humidified sample (48 square inches) of wallboard. Two specimens
are tested: one having been in a humidifier for two hours, and one
having been in a humidifier for 20 hours. Each specimen shows a
minimum moisture reading of "50 plus" with a Data Tech moisture
meter upon completion of each respective humidification period (or
a reading of between 28 and 34 after two hours of humidification
and 50 maximum scale reading after 20 hours of humidification, as
measured by a Sensortech Model PMT-110 meter). After
humidification, a sample is scored across the width of the board on
one side (i.e., one surface paper), the wallboard core is broken at
the score line, and then the surface paper is pulled from the
wallboard core on each end of the broken sample. The procedure is
repeated by scoring the opposite surface paper in a distant portion
of the sample and similarly pulling the surface paper from the
wallboard core. The bond failure is evaluated by inspection.
[0081] Results of the foregoing tests are tabulated below in Table
III. With the exception of the nail pull test, the lower the
reported number, the better is the result and, hence, the better
the wallboard quality.
3TABLE III Test Prior Art Embodiment of Invention Nail Pull
Resistance 89.8 lb (40.7 kg-force) 88.0 lb (39.9 kg-force) End Peel
0.33 inch (0.84 cm) 0.19 inch (0.48 cm) Score & Snap hot at
take-off - as is 1/16 inch (0.16 cm) 1/16 inch (0.16 cm) hot and
flexed 1/4 inch (0.64 cm) 1/8 inch (0.32 cm) Shear Width hot at
take-off 3.79 inches (9.63 cm) 3.32 inches (8.43 cm) overnight 4.63
inches (11.76 cm) 3.29 inches (8.36 cm) conditioned Shear Split hot
at take-off 0.84 inch (2.1 cm) 0.36 inch (0.91 cm) overnight 1.63
inch (4.14 cm) 0.79 inch (2.01 cm) conditioned Humidified Bond 79%
peel 18% peel
[0082] The results of Examples 1 and 2 demonstrate that a core
composition according to the invention produces lightweight gypsum
articles having strength and quality characteristics comparable to,
and in some cases better than, heavier gypsum articles of the prior
art. Other properties of wallboard articles produced according to
the invention may also be benefited by use of the inventive methods
and compositions, including transverse load strengths, sag
resistance, 90.degree. pull force resistance, and core tensile
strength. In addition, the inventive compositions and methods may
advantageously provide these strengths over substantial periods of
time and at humidified conditions.
[0083] All of the compositions and/or methods and/or processes
and/or apparatus disclosed and claimed herein can be made and
executed without undue experimentation in light of the present
disclosure. While the compositions and methods of this invention
have been described in terms of preferred embodiments, it will be
apparent to those of skill in the art that variations may be
applied to the compositions and/or methods and/or apparatus and/or
processes and in the steps or in the sequence of steps of the
methods and/or processes described herein without departing from
the concept, spirit and scope of the invention. All such similar
substitutes and modifications apparent to those skilled in the art
are deemed to be within the spirit, scope and concept of the
invention.
* * * * *